1. Field of the Invention
The present invention is directed to an expandable and curable polyester composition, the method for making same and the product of said method. More specifically, the present invention is directed to an expandable and curable polyester composition comprising a mixture of a liquid, ethylenically unsaturated polyester resin composition; a peroxide; an organometallic promoter; and a dialky hydrazine or a trialkyl hydrazine, and the method for making same.
2. Description of the Prior Art
There are several references to expandable and curable polyester compositions employed and to methods to prepare said expandable and curable polyester compositions. These methods usually include foaming and crosslinking as separate operations. Either a foam is prepared then crosslinked without destroying it, or the resin is crosslinked while gas is released into it. In either of the approaches the gas may be provided by a variety of means. Other methods use certain chemicals acting as curing and/or foaming agents, but their commercial application has been greatly hindered by extreme stability and/or toxicity problems or lack of practicality.
Certain references of interest disclose the syntheses of foamable and curable polyester compositions. U.S. Pat. No. 3,410,719, issued Nov. 12. 1968 (Roper) teaches the preparation of non-foamed solid acrylic-type coating compositions employing certain alkyl- or arylhydrazines in combination with either a peroxide or an organic salt.
U.S. Pat. No. 3,920,589, issued Nov. 18, 1975, (Jacobs et al.) deals with a method for expanding unsaturated polyester resins using certain sulfonylhydrazides, a peroxide catalyst, a cobalt accelerator and a redox halogen-containing compound. Closely related U.S. Pat. No. 3,920,590, issued Nov. 18, 1975, (Jacobs et al.) deals with the expansion and curing of unsaturated polyesters using 4,4-oxybis(benzenesulfonyl) hydrazide, hydrazine, together with 5 to 30 times the normal level of peroxide and metal organic salt normally used for the cure of such polyester. It is noted that this method does not require the addition of any redox compound. Yet another closely related method, U.S. Pat. No. 3,920,591, also issued on Nov. 18, 1975 (Jacobs et al.), discloses a method for the expansion and cure of unsaturated polyester resins employing a combination of sulfonyl hydrazines, peroxides and amines.
The method of Kamens et al. for making an expandable and curable polyester, published in U.S. Pat. No. 3,993,609, issued Nov. 23, 1976, comprises the use of certain acid sensitive azo compounds such as 2-t-butylazo-2-hydroxybutane, a curing agent, such as a peroxide, and a promotor such as copper naphthenate. It is known that azo compounds are difficult to handle, require refrigeration and provide very short pot lives.
A process for making textured foam thermoplastic sheets for reaction of sulfonyl carboxyl hydrazines or 1,1-dialkyl hydrazines with a peroxide by heating the plastic sheet containing both materials is taught in U.S. Pat. No. 3,574,665 issued to Kwart et al.
Neither the methods of the references above nor any other processes known have proved to be a commercial success because of high cost or impracticality. It is believed that the instant invention is a significant improvement over previous methods and provides industry with a viable and practical method for making foamed and cured polyester products at reduced cost.
Recently an improved expandable and curable polyester composition, useful in providing an improved method for simultaneously foaming and curing a polyester resin has been developed.
This method is set out in pending U.S. patent application, Ser. No. 219,420, filed Dec. 22, 1980. The foamable and curable polyester composition disclosed in this application includes a liquid unsaturated polyester resin, an organic peroxide or hydroperoxide, an organo metallic promoter for the peroxide and a sulfonyl hydrazide blowing agent.
A still earlier copending application, Ser. No. 186,099, filed Sept. 11, 1980 by Stott and Wheeler, and assigned to the same assignee as the present application, discloses a method for making a cured and expanded polyester resin. It is also directed to a curable and crosslinkable composition useful in such a method which includes mixture of a liquid unsaturated polyester resin, a peroxide, a metal salt of an organic acid capable of promoting the compositions of peroxide and a compound selected from the group consisting of monoalkylhydrazine and hydrazone. Again, this composition, useful in the method of forming a foamed polyester resin, represents an advance in the art. However, monoalkylhydrazines or hydrazones require special handling conditions.
In summary, until the disclosures set forth in the latter two applications, there were no chemical compounds or mixtures reported which met all the necessary criteria for good shelf life, good pot life in the resins, compatibility with standard resin processing equipment and the ability to produce uniform essentially crack-free foams from a wide range of general purpose unsaturated polyester resins. With the introduction of the two applications mentioned immediately above, the problems of the prior art were substantially alleviated. However, problems associated with the hydazine component in the expandable and curable polyester composition mixture still exists. These mixtures are either not as stable, or not as efficient as one would wish.